Human knee joints endure exceptional loads and a wide variety of loading scenarios throughout the life of an individual. While the human knee joint is capable of supporting most of these typical loads under normal conditions for the life of the individual, in certain circumstances the human knee joint suffers degraded performance. For instance, injury can occur to the knee causing the knee to not fully repair itself, or not being fully repairable through medical intervention, such that it becomes beneficial to replace the knee joint with an artificial knee joint. In other circumstances, degenerative disease can act on the natural knee joint to degrade its performance in an irreversible fashion, such that replacement of the natural knee joint with an artificial knee joint is indicated.
Artificial knee joints are well known in the literature and have come into widespread use. In general, such artificial knee joints include a femoral component, a tibial component and a patellar component. The distal end of the femur is surgically prepared to have the distal end thereof have a contour matching an internal box surface of the femoral component. The femoral component is then attached to the distal end of the femur. Similarly, the proximal end of the tibia is prepared, typically by cutting a flat proximal surface on the proximal end of the tibia, and the tibial component is attached to this proximal end of the tibia. Muscles and ligaments surrounding the knee are disturbed as little as possible so that they can continue to function in the same manner that they do with a natural knee joint. Proximal surfaces of the tibial component and distal surfaces of the femoral component abut each other and are designed to facilitate articulation relative to each other in the same way that the distal end of a natural femur articulates relative to the proximal end of a natural tibia. Typically, an insert of materials somewhat more flexible and resilient than metal is attached to a proximal end of the tibial component, with other portions of the tibial component formed of a more rigid material, such as titanium or cobalt chrome. This insert in some ways duplicates the function of a natural meniscus within a natural knee joint, and helps to minimize friction in the articulation of the femoral component relative to the tibial component.
Numerous drawbacks have been noted with prior art artificial knee joints and for which this invention strives to provide a significant and beneficial improvement. For instance, artificial knee joints are known for being somewhat complex to implant, and most particularly the femoral component. In particular, the distal end of the femur must be extensively shaped to properly mate with facets on the internal box face of the femoral component.
In the prior art, the surgeon must make numerous very precise cuts on the distal end of the femur and these cuts vary based on the particular geometry of the facets on the internal box face of the femoral component. Because different human bodies have different sizes, various different femoral components having different sizes must be considered before selecting the particular femoral component. Typically, a cutting jig or other specialized tool must be selected that matches with the femoral component selected so that the cuts are properly made.
As a result, the surgeon, manufacturer or an associated health care facility must maintain an extensive inventory of femoral cutting jigs for potential use in an artificial knee joint surgical procedure. Such extensive inventory of cutting jigs is expensive to maintain, requires additional space within the surgery room or nearby, and presents the greater possibility of problems during or after surgery. Furthermore, an increase of such cutting jigs is more difficult to clean and sterilize which increases the potential for infection, in turn resulting in a less than fully desirable outcome. U.S. Pat. Nos. 5,925,049 and 5,749,876 both describe a femoral cutting instrument sizer that allows a single tool to be used for a set of femoral components of different sizes however both devices are cumbersome and complicated to use. Accordingly, a need exists for an artificial knee joint which has a femoral component which is one of a set of femoral components of different sizes which share as many shape and size characteristics as possible, as well as a single tool which can easily make the necessary cuts for all different femoral component sizes.
Another problem with known prior art artificial knee joints is that they cannot duplicate the large amount of flexion produced by a natural human knee joint and still provide sufficient contact between the artificial femur and the tibial component. Conventional artificial knee joints are limited in further flexion because they typically cause the femur or structure coupled to the femur to abut the tibia or structures coupled to the tibia to prevent further flexion. Accordingly, a need exists for an artificial knee joint which can provide as much flexion as possible to more fully mimic a natural knee joint in performance.
Another problem with known prior art artificial knee joints is their inability or difficulty in facilitating knee pivoting rotation in both clockwise and counterclockwise directions. A natural knee joint is capable of a small amount of pivoting rotation. Such pivoting rotation is particularly desirable when a person is walking along a curving path.
Some artificial knee joints, such as those taught by Hodge (U.S. Pat. No. 5,413,604) allow for pivoting rotation of the medial condyle about the lateral condyle, but not rotation of the lateral condyle. Furthermore, other artificial knee joints, such as those taught by Kaufman (U.S. Pat. No. 6,013,103) and Tuke (U.S. Pat. No. 5,219,362) describe pivoting rotation of the lateral condyle about the medial condyle. Accordingly, a need exists for complete replication of function of a natural knee joint, including pivoting rotation in both directions.
Another problem with known prior art artificial knee joints is the need for the insert or other meniscal structure to exhibit a minimum thickness for suitable wear characteristics and duration, while minimizing an amount of bone required to be removed from the proximal end of the tibia. Generally speaking, bone is removed from the proximal end of the natural tibia in an amount equaling a height of portions of the tibial component of the artificial knee joint which extend beyond the proximal surface of the tibia after it has been prepared for receiving the tibial component. Typically, regulatory authorities recommend a six millimeter thickness on the insert or other meniscal wear structure, and structural portions of the tibial component need approximately four millimeters for sufficient strength, a full ten millimeters of bone must be removed from the proximal tibia to maintain proper ligament tension and maintain patient leg length. It is desirable to remove as little natural bone as possible, as natural bone is beneficial in many respects and to be preferred over artificial structures to the extent possible.
Prior art attempts have been made to nest the insert into the tibial component somewhat, but only with joints that prevent twisting. See for instance patent to Aubriot (U.S. Pat. No. 5,326,358) and Johnson (U.S. Pat. No. 4,568,348). Accordingly, a need exists for a tibial component of an artificial knee joint which can maintain the regulatory recommended thickness of an insert or other wear structure while minimizing a height of other portions of the tibial component of the artificial knee joint, and still allow twisting, to minimize the amount of required bone removal from the proximal end of the tibia.